Synonyms of insidious

insidious

adjective

as in treacherous

formal causing harm in a way that is gradual or not easily noticed

Most people with this insidious disease have no idea that they are infected.

an insidious enemy

Related Words

• treacherous
• subtle
• false
• deceptive
• perfidious
• incorrect
• wrong
• misleading
• deceitful
• cunning
• specious
• delusive
• wily
• beguiling
• sneaky
• fallacious
• ambiguous
• devious
• perplexing
• trick
• underhanded
• crafty
• shady
• tricky
• sly
• artful
• subtile
• deceiving
• delusory
• fast
• fraudulent
• puzzling
• underhand
• distracting
• confounding
• sneaking
• inaccurate
• shifty
• slick
• artificial
• foxy
• mendacious
• guileful
• duplicitous
• deluding
• untrustworthy
• trickish
• bewildering
• lying
• dishonest
• untruthful
• evasive
• faithless
• spurious
• bogus
• crooked
• counterfeit
• hypocritical
• knavish
• fake
• phony
• circuitous
• sham
• feigned
• ambidextrous
• dissembling
• forged
• equivocal
• insincere
• double-dealing
• jive
• backhanded
• defrauding
• two-faced
• left-handed

Dissimilar Words

• direct
• plain
• outspoken
• frank
• open
• candid
• illuminating
• straight
• explanatory
• revealing
• revelatory
• clarifying
• free-spoken
• truthful
• openhearted
• plainspoken
• honest
• elucidative
• trustworthy
• foursquare
• straightforward
• forthright
• aboveboard
• nondeceptive

Example Sentences

Recent Examples of insidious

In my view, statements to that effect are shortsighted, prioritizing short-term social effects over more insidious and long-term issues, including addiction. — Emma Fenske, The Conversation, 2 July 2026

The narrative chronicled an international gang of scientists and military folks that stumble across a Stargate network deep in the Pegasus Galaxy and its insidious alien antagonists called The Wraith. — Jeff Spry, Space.com, 17 June 2026

This reflects a larger and perhaps insidious problem in the United States, where there’s been an erosion in trust in public health, in doctors and in the medical profession as a whole. — Joshua P. Cohen, Forbes.com, 13 June 2026

Speaking of pop music, while the new ad format is expected to have its critics, there’s a far more insidious change afoot in that Green and Pleasant Land. — Anthony Crupi, Sportico.com, 12 June 2026